The agency gives a medication priority review when it's believed to have the potential to be much better than existing therapies. In clinical trials of Lucentis, which is injected directly into the eyeball, patients with wet age-related macular degeneration saw their vision loss stop, and some even had an improvement.

Another trial found Lucentis to be more effective than Visudyne, a treatment from QLT ( QLTI) and Novartis ( NVS), using to a head-to-head comparison.

"The FDA's decision to grant priority review underscores the potential significant advancement of Lucentis in the treatment of wet AMD and puts us one step closer to making available a therapy that may change outcomes for people with this devastating disease," said Hal Barron, Genentech's chief medical officer.

AMD is a degenerative disease that causes central vision to get progressively worse. Macular degeneration is the most common cause of vision loss in people older than 55. Wet AMD accounts for about 10% of all cases and is marked by abnormal blood vessel growth beneath the center part of the retina.